Airborne transmitting antenna

ABSTRACT

AN AIRBORNE TRANSMITTING ANTENNA ASSEMBLY HAVING A DIELECTRIC BASE PORTION IS PROVIDED WITH ESSENTIALLY FLAT CONDUTORS THAT ARE EDGE-MOUNTED ONTO THE DIELECTRIC TO OBTAIN A SIGNIFICANTLY INCREASED POWER-HANDLING CAPABILITY WITHOUT ADVERSELY AFFECTING OTHER ANTENNA PERFORMANCE CHARACTERISTICS SUCH AS RADIATION PATTERNS, RADIATION AXIAL RATIOS, AND THE LIKE.

Feb. 16,1971 J. D. LEONARD H AIRBORNE TRANSMITTING ANTENNA Filed Nov. 8,1967 Fi m 4 FREQUENCY IN GIGAHERTZ United States Patent 3,564,553AIRBORNE TRANSMITTING ANTENNA James D. Leonard, Columbus, Ohio, assignorto North American Rockwell Corporation Filed Nov. 8, 1967, Ser. No.681,462 Int. Cl. H01q 11/10, 1/36 US. Cl. 343-792.5 3 Claims ABSTRACT OFTHE DISCLOSURE SUMMARY The airborne transmitting antenna of thisinvention, in a preferred embodiment, is comprised of a conicallyshapeddielectric base that supports a balun feed device and that is providedat its exterior surface with spiral conductors; such conductors areconnected to the balun in electrically-conducting relation and radiatethe desired radio frequency electromagnetic energy field. The spiralconductor elements are also normally fabricated of essentially fiatmetallic material and are mounted on the dielectric base in anedge-wound manner, as by the engagement of relatively narrow edgeregions of each conductor with corresponding comparatively-shallowgroove sections provided in the dielectric base exterior surface.

DRAWING DESCRIPTION FIG. 1 is a perspective view of a type of aircraftsystem to which the instant invention has application;

FIG. 2 is a sectional view of an airborne transmitting antennainstallation in the aircraft system of FIG. 1 and having an antennaassembly ofthis invention incorporated therein;

FIG. 3 is an enlarged elevational view of the antenna assemblyillustrated in FIG. 2;

FIG. 4 is a sectional view of the antenna assembly of FIGS. 2 and 3;

FIG. 5 is a perspective view of the apex conductor connections shown inelevation in FIGS. 3 and 4;

FIG. 6 is a plan view of the conductor connections shown in elevation inFIGS. 3 and 4;

FIG. 7 is a graph illustrating a power-handling capability increaseobtained by practicing the instant invention; and

FIG. 8 is a graph illustrating a voltage standing wave ratiocharacteristic obtained by practicing the instant invention.

DETAILED DESCRIPTION FIG. 1 illustrates an aircraft system 10 having anairborne transmitting antenna installation 11 of a type to which theinstant invention has application. Installation 11, in representativeapplications, is provided for use in connection with on-boardcommunication equipment, electronic countermeasures equipment, or thelike. As shown in FIG. 2, installation 11 includes antenna 12 of thisinvention, such antenna in the illustrated installation being secured tocavity-defining support 13 by fasteners 14. Support 13 is carried byairframe structure 15 and is secured in position by the fastenersdesignated 16. In most applications a radiation absorber material 17 isprovided interiorly of support 13 to prevent energy radiated by antenna12 into the interior of the cavity from adversely affecting the antennaperformance. Antenna 12 is operatively connected ice to coaxial RFenergy feed 18 by coupling 19. A radiationtransparent member 20 may besecured to aircraft structure 15 by fasteners 16 also but is providedessentially for fairing and energy transmission purposes.

Antenna 12, in the preferred embodiment of FIGS. 3 and 4, is comprisedof a comically-shaped dielectric base 21, a balun feed device 22, andspiral conductors 23 and 24. Dielectric base 21 is comprised of supportmember 25, cone member 26, and retainer 27 joined together by adhesivebonding or the like.

Balun device 22 is positioned within support 25 and is of conventionalconstruction. In the FIG. 4 illustration, balun 22 is illustrated ashaving a tubular outer conductor 28, a rod-like inner conductor 29, anda dielectric insulating member 30 that separates the conductor elements. The uppermost portion of balun 22 projects through support 25 andalso in-part through cone element 26. A dielectric insulating sleeve 31is provided in surrounding relation to the uppermost portion of balun 22in the region interior of cone member 26. Also as shown inPIG. 4,dielectric base retainer element 27 is preferably provided with recessessuch as 32 that receive nut elements 33 intended for cooperation withfasteners 14. A metallic mounting plate 34 having openings 35 alignedfor fasteners '14- is secured to retainer 27 by separate fasteners suchas rivet 36. Conductors 23 and 24 each have a spiral configuration andare normally fabricated from essentially fiat metallic material byselective chemical etching. The exact spiral configuration, such as alogarithmic spiral, is developed using known antenna configurationtechniques and is not critical to the instant invention, However, inapplications involving the present invention, the radial cross-sectionof each conductor element 23,24 is considerably greater in width thanthickness. See FIG. 4 for example.

Cone member 26 may be made of any of numerous different dielectricmaterials depending upon specific application operating temperaturerequirements and the like. For moderate service temperatures, cone 26has been fabricated of conventional glass reinforced phenoliccompositions. The continuous comparatively-shallow grooves 37, 38provided in the exterior surface of cone 26 for engagement withrelatively narrow edge regions of conductors 23, 24 may be developed bymachining. In instances where come 26 is made of a high-temperaturematerial such as a ceramic, grooves 37 and 38 may be developed in thecourse of a molding operation. FIGS. 5 and 6 illustrate details forconnecting conductor elements 23 and 24 to the conductive elements ofbalun device 22. Conductor '23, for instance, cooperates with oversizeslot 39 in the projecting portion of the dielectric insulating member 30and is joined to inner conductor 29 of balun 22 in electricallyconducting relation. Conductor 24, on the other hand, is secured toouter conductor 28 at recess region 40 also in an electricallyconducting relation. The free terminations of conductors 23 and 24- maybe arranged to cooperate with openings such as 42 and 43 in the lowerregion of cone member 26.

The performance advantages that may be obtained by the practice of theinstant invention in comparison to conventional antenna constructionsare substantiated by the test data of FIGS. 7 and 8. Power-handlingcapability comparisons (curves 44 and 45 of FIG. 7) and on-axis voltagestanding wave ratio comparisons (curves 46 and 47 of FIG. 8) wereobtained in connection with testing a conical spiral antenna made inaccordance with the instant invention and a conventional flat-woundantenna of similar conical configuration, each to voltage breakdownunder substantially identical operating conditions. The improved antennaincluded a conical base with an apex angle of approximately 29 and withan overall on-axis height of approximately 4.5; the dielectric materialutilized was a glass/ phenolic laminate system molded to a wallthickness of from 0.030 to 0.050" in matched metal tooling. The balunouter conductor in the im: proved antenna was fabricated of brass andthe center conductor was silver plated copper Weld wire. Both were goldplated. The balun dielectric was machined from isostatically molded,thermally stable polytetrafiuoroethylene, Also in the tested antenna ofthis invention, the conductors 23, 24 were chemically etched using aphotosensitive resist and standard chemical milling techniques todevelop logarithmic spiral configurations in essentially flat copperstock approximately 0.020" thick. The reference antenna was providedwith the same conical base dimensions and details except that theconductors were placed on the cone member exterior surface in aconventional flat-wound manner.

As shown by FIG. 7, curve 44, the improved antenna with edge-woundconductors in accordance with the instant invention exhibited apower-handling capability of approximately 120 watts without voltagebreakdown between adjacent conductors over the frequency range of 2 to 8gHz. in a simulated environment of 70,000 altitude and at an elevatedtemperature of 250 F. As shown by curve 45, the conventional fiat-woundantenna operated with a power-handling capability of only approximately20 watts under the described conditions and over the indicated frequencybandwidth. Thus, by practicing the instant invention and takingadvantage of permitted increased spacing between turns, particularly inthe cone apex region, and heavier conductor cross-sections, thepower-handling capability of the conventional antenna may be increasedapproximately six-fold.

Curves 46 and 47 of FIG. 8 illustrate the voltage standing wave ratiomeasured along the antenna axis for the described antenna of thisinvention and for a comparable conventional fiat-wound antenna,respectively. It is clear from FIG. 8 that no degradation of performanceoccurs with respect to achieving voltage standing wave ratios less than2 over comparable operating bandwidths. Similarly, testing hasestablished that no radiation pattern degradation occurs as a result ofthe improved conductor arrangement.

I claim:

' 1. A transmitting antenna for radiating a radio-frequencyelectromagnetic field having an amplitude pattern about the radiationaxis of the antenna, and comprising in combination:

(a) feed means receiving radio-frequency electrical energy for radiationas an electromagnetic field,

(b) dielectric base means having a substantially conical exteriorsurface that is geometrically defined with reference to the antennaradiation axis, and

(c) logarithmically periodic spiral conductor means mounted on saiddielectric base means and having an essentially rectangularcross-section and an inner edge surface that is narrow in comparison toconductor surface portions adjacent said inner edge surface, said spiralconductor means being mounted on said dielectric base means withsubstantially only said narrow inner edge surface at and in saiddielectric base means conical exterior surface and being electricallyconnected to said feed means to radiate radio-frequency electricalenergy received therefrom as a radio-frequency electromagnetic fieldhaving an amplitude pattern about the radiation axis of'the antenna.

- 2. The invention defined by claim 1, wherein said dielectric basemeans is provided in said conical exterior surface with a shallow spiralgroove of width substantially equal to the width of said conductor meansnarrow edge surface, said conductor means being mounted on saiddielectric base means in engagement with said shallow spiral groove.

3. The invention defined by claim 1, wherein said spiral conductor meansadjacent surface portions include surface elements that, at conductorcross-sections, are along straight lines extending outwardly from saidnarrow inner edge surface, said spiral conductor means being mounted onsaid dielectric base means with said surface elements positionedsubstantially at right angles to the radiation axis of the antenna.

References Cited UNITED STATES PATENTS 2,871,478 1/1959 Lander 343-895X2,958,081 10/1960 Dyson 343--895 3,188,643 6/1965 Dyson et al 3438953,230,540 1/1966 Keiji Endo et al. 343--895 HERMAN KARL SAALBACH,Primary Examiner T. VEZEAU, Assistant Examiner U.S. Cl. X.R.

